Reactions of metal carbonyl derivatives. Part XII. The synthesis of some cationic bridged halogeno-derivatives of ruthenium and their reactivity towards certain nucleophiles

Abstract

A study of the halogenation of [{Ru(π-C₅H₅)(CO)₂}₂] has revealed that while neutral [Ru(π-C₅H₅)(CO)₂X](X = Cl, Br, or I) is formed in solvents such as dichloromethane and chloroform, salts of the cation [{Ru(π-C₅H₅)(CO)₂}₂X]⁺ separate from those reactions performed in benzene or toluene and in the presence of large counterions such as PF₆^–. It is shown that the cationic species [{Ru(π-C₅H₅)(CO)₂}₂X]⁺ is readily susceptible to attack by halides and pseudo-halides to yield products according to the scheme [{Ru(π-C₅H₅)(CO)₂}₂X]⁺+ Y^–→[Ru(π-C₅H₅)(CO)₂X]+[Ru(π-C₅H₅)(CO)₂Y] The mechanism of formation of [Ru(π-C₅H₅)(CO)₂X] from [{Ru(π-C₅H₅)(CO)₂}₂] is discussed in terms of this scheme. The cations [{Ru(π-C₅H₅)(CO)₂}₂X]⁺(X = Cl and Br) also react readily with the anion BPh₄^–. Fission of a boron–carbon bond in BPh₄^– and transfer of a phenyl group to a ruthenium atom is effected, to yield [Ru(π-C₅H₅)(CO)₂Ph] and [Ru(π-C₅H₅)(CO)₂X]. The cyanide and not a phenyl group is extracted from BPh₃CN^– on reaction with [{Ru(π-C₅H₅)(CO)₂}₂X]⁺(X = Cl or Br) in acetone under reflux to give [Ru(π-C₅H₅)(CO)₂CN] and [Ru(π-C₅H₅)(CO)₂X]; the zwitterionic species [Ru⁺(π-C₅H₅)(CO)₂NCB-Ph₃] is shown to be an intermediate in the reaction.